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Questions and Answers
The disodium salt of EDTA is freely soluble in water.
The disodium salt of EDTA is freely soluble in water.
True
EDTA is a bidentate ligand containing 2 oxygen and 2 nitrogen donor atoms.
EDTA is a bidentate ligand containing 2 oxygen and 2 nitrogen donor atoms.
False
EDTA reacts with metal ions in a 2:1 ratio.
EDTA reacts with metal ions in a 2:1 ratio.
False
EDTA is a selective chelating agent.
EDTA is a selective chelating agent.
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The stability of the metal-EDTA complex increases in acidic medium.
The stability of the metal-EDTA complex increases in acidic medium.
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Murexide is a metallochromic indicator that forms a colorless complex with metal ions.
Murexide is a metallochromic indicator that forms a colorless complex with metal ions.
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Eriochrome Black T (EBT) is a pH-independent metal indicator.
Eriochrome Black T (EBT) is a pH-independent metal indicator.
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The stability of the metal-EDTA complex is lower than the metal-indicator complex.
The stability of the metal-EDTA complex is lower than the metal-indicator complex.
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The bond between the metal ion and the ligand in a complex is a covalent bond.
The bond between the metal ion and the ligand in a complex is a covalent bond.
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Coordination number is always an odd number.
Coordination number is always an odd number.
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NH3 is a unidentate ligand.
NH3 is a unidentate ligand.
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The higher the valence of the metal ion, the less stable the complex.
The higher the valence of the metal ion, the less stable the complex.
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The Lewis acid is the electron donor in a complex.
The Lewis acid is the electron donor in a complex.
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Ag+ forms 4 coordinate bonds.
Ag+ forms 4 coordinate bonds.
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A bidentate ligand is attached to a metal at three sites.
A bidentate ligand is attached to a metal at three sites.
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Polydentate ligands are preferred as titrants due to their ability to form weak complexes.
Polydentate ligands are preferred as titrants due to their ability to form weak complexes.
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Chelation is a type of complexation where ligands possess only one donor group.
Chelation is a type of complexation where ligands possess only one donor group.
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EDTA is a type of ligand that forms water-insoluble chelates.
EDTA is a type of ligand that forms water-insoluble chelates.
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A metal with an incomplete subshell will produce unstable complexes.
A metal with an incomplete subshell will produce unstable complexes.
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A large ionic radius of a metal increases the stability of a complex.
A large ionic radius of a metal increases the stability of a complex.
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A ligand with a high ionic radius increases the stability of a complex.
A ligand with a high ionic radius increases the stability of a complex.
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EDTA is used as a ligand for a limited number of metal ions.
EDTA is used as a ligand for a limited number of metal ions.
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Study Notes
EDTA (Ethylene Diamine Tetracetic Acid)
- Symbol: H2y2-
- Disodium salt is freely soluble in water: Na2H2y → 2Na+ + H2y2-
- Hexadentate ligand containing 4 oxygen and 2 nitrogen donor atoms
- Reacts with metal in a 1:1 ratio
- Non-selective chelating agent
Reaction with Metal Ions
- M2+ + H2y2- → My2- + 2H+
- M3+ + H2y2- → My- + 2H+
- M4+ + H2y2- → My + 2H+
Factors Affecting Stability of the Complex
- Metal Factors:
- Type of metal: Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+ are strongest to attract ligands
- Ionic radius: Small ionic radius increases stability
- Electric charge: High electric charge produces stable complexes
- Ligand Factors:
- Basic character (ability of electron donation) increases stability
- Ionic radius: Large ionic radius increases stability
Indicators
- Metal Indicators (metallochromic indicator)
- Form colored complexes with metal ions
- Reversible complexation reaction
- Color of free form is different from complexed form
- Stability of Metal-Indicator complex is lower than Metal-EDTA complex
- Examples of Metal Indicators:
- Murexide (H4In- ↔ H3In2- ↔ H2In3-)
- Free form has different color according to pH of the medium
- Complex form has different color according to the type of metal ion
- Eriochrome Black T (EBT)
- Murexide (H4In- ↔ H3In2- ↔ H2In3-)
Polydentate Ligands
- Bidentate Ligand: Attached to metal at two sites (e.g., ethylene diamine)
- Tridentate Ligand: Attached to metal at three sites (e.g., diethylene triamine)
- Tetradentate Ligand: Attached to metal at four sites (e.g., triethylene tetramine)
- Polydentate ligands are preferred as titrants due to:
- Complexes formed are more stable
- Reaction is complete in one step, leading to a sharp end point
Chelation and Complexometry
- Chelation: Type of complexation where ligands possess two or more donor groups
- Ligands combine with metal to form ring structure compounds called metal chelates
- Metal chelates are usually water-insoluble, except for sequestering agents like EDTA
- Complexometry: Type of quantitative analysis where the compound to be analyzed forms a slightly ionized complex
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Description
EDTA, a hexadentate ligand, reacts with metal ions in a 1:1 ratio, forming a metal-EDTA complex. It is a non-selective chelating agent, but its ionization and stability are affected by acidic medium.
